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Photometry of SN 2017cts/ASASSN-17em

ATel #10251; R. Konyves-Toth, J. Vinko (Konkoly Obs)
on 8 Apr 2017; 08:12 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)

Subjects: Optical, Supernovae

We report photometric observations of the recently discovered Type Ia supernova SN 2017cts/ASASSN-17em (ATel #10241, #10242) taken with the 60/90 cm Schmidt telescope through Bessell B,V,R,I filters at Konkoly Observatory, Piszkesteto, Hungary on 2017 Apr 06.9 UT.

Photometry on the SN and several local comparison stars was computed via PSF-fitting. The magnitudes of the local comparison stars were tied to their PS1-photometry after transforming the PS1 griz magnitudes to the Johnson-Cousins BVRI system (Magnier et al. arXiv:1612.05242).

The following Vega-magnitudes have been obtained for SN 2017cts:

  MJD      B     eB      V     eV       R    eR      I     eI 
57849.94 16.107 0.059  16.165 0.011  16.043 0.029  16.079 0.027 

Our data indicate that the SN has brightened by about 1 mag since its discovery on 2017-04-02.46 UT (ATel #10241), confirming its pre-maximum phase reported by D. Bersier (ATel #10242).

The color indices of SN 2017cts, after correcting for Milky-Way extinction, are B-V = -0.086, V-R = 0.104 and V-I = 0.048, suggesting a normal Type Ia supernova close to maximum light.

Adopting the Hubble-flow distance D(3K CMB) = 80.7 +/- 5.7 Mpc for the presumed host galaxy CGCG 299-048 NED01, the extinction-corrected absolute magnitudes of the SN are M_B = -18.54 (+/-0.16), M_V = -18.45 (0.15), M_R = -18.55 (0.15) and M_I = -18.50 (0.15) mag, consistent with those of a Type Ia supernova before maximum light.